Improvement in wooden truss-bridges



TA. w. PRATT. 4Wooden Truss Bidges Patented Aprl, 1873.

AM PHoro-'umasRA/Hm cn Mx (assum Pnoces IUNITED STATES PATENT OFFICE.

THOMAS wILLIS PRATT, on BOSTON, MAssAoi-rusnTTs.` e

IMPROVEMENT IN WOODEN TRUSS-BRIDGES.`

Specification forming part of Letters Patent No. 137,482, dated April 1, 1873 5 application filed January 16, 1873.

To all 'whom it may concern:

Be it known that I, THOMAS WILLIS PRATT, of Boston, in the county of Suffolk and State of Massachusetts, have invented certain Improvements in Wooden Truss-Bridges; of which the following is a full, clear, and eX- act description, reference being had to the accompanying drawing making part of this specication, in which- Figure 1 is a perspective view of a section of a wooden bridge constructed in accordance with my invention. Fig. 2 is a vertical transverse section enlarged through the same. Fig. 3 is a horizontal transverse section on the line :v :v of Fig. 2.

My present invention relates tothe construction of wooden truss-bridges; andconsists in a series of triangular trusses formed by the union of strut and tension braces with upper and lower horizontal chords, the material employed in their construction be` ing a series of planks, which are placed side by side to form the braces, and which are placed upon each other, breaking joints, to form the chords, the extremities ofthe braces lapping on each other, and their tops being secured together and to the upper chord; while the bottoms of the braces are secured together and to the lower chord, thus forming a strong uninterrupted bond or connection throughout the entire length of the bridge. My invention also consists in stift'- ening and preventing the lateral deflection of the braces by means of clamps and studs applied at or near theirY centers, the parts being securely connected by bolts or otherwlse.

l'lo enable others skilled in the art to understand and use my invention, I will proceed to describe the manner in which I have carried it out.

In the said drawing, A represents the upper chord, composed of a series of planks, grouped together into three separate and 1ndependent lines, a b c, extending horizontally from the tops of vertical beams or frames (not shown) rising from a bolster, 4, resting on the abutment (not shown). The middle line b of the upper chord is composed of four rows of planks; and the outer lines a and c each are composed of two rows of planks, strongly secured together, and so arranged as to break joints; a space, d, being formed between the middle line b and each line a and c, into which space project the upper ends of' the strut-braces C and tension-braces D, the tops of two consecutive braces, C D, lapping on each other, and being securely connected together and to the middle line b and outer line et or c of the upper chord A by tree-nails 5. The lower chord E is also constructed in like manner and of the same material as the upper chord A; and the lower ends ot' the planks of the two consecutive braces lap on and are secured, by tree-nails 6, to each other and to the middle line b and outer line a or c ot' the series of plank forming the lower chord E.

To prevent the lateral deflection of' the braces C D in either direction, and to stiffen them, I employ clamps e and studs h in the following manner: The planks forming the two opposite sides of each brace are sprung slightly outward or apart from each other at or near their center, and a pair of horizontal studs, h, are placed between` them, both ends of the studs resting in sockets or openings formed in plates t', which, together with similar plates k-one on the outside of each set of planks-are held in place by bolts Z and nuts m. (See Fig. 3.)

The studs prevent-the planks from being upset or bent inward; and the plates z', bolts l, and nuts m serve as clamps e for holding the opposite planks together and preventing their spreading apart.

' From the foregoing construction it will be seen that a continuons bond of the parts is formed the whole length of i the bridge of sufficient Strength and stiffness to withstand any strain to which it is ever intended to be subjected.

Claims.

What I claim as my invention, and desire to secure lby Letters Patent, is-

1. A wooden truss-bridge, in which the braces are arranged in a series of triangles by grouping planks together in sets of two or more as the strain increases, and lapping each other at their intersection, and thoroughly se With studs between the braces secured by metoured to the upper and lower chords and to a1 bolts, substantiallyin the manner described.

each other, substantially in the manner de- Witness my hand this 6th day of Deeember,

scribed. A. D. 1872.

2. The mode of stiffening the braoeslater- THOMAS WILLIS PRATT. ally by springing them outward or apart from v In presence ofeach other at or near their center, and seour- N. W. STEARNS, ingthem in that position by the use of clamps, W. J. GAMBRIDGE. 

